WO2011013228A1 - 非水電解液二次電池 - Google Patents
非水電解液二次電池 Download PDFInfo
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- WO2011013228A1 WO2011013228A1 PCT/JP2009/063575 JP2009063575W WO2011013228A1 WO 2011013228 A1 WO2011013228 A1 WO 2011013228A1 JP 2009063575 W JP2009063575 W JP 2009063575W WO 2011013228 A1 WO2011013228 A1 WO 2011013228A1
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M4/00—Electrodes
- H01M4/02—Electrodes composed of, or comprising, active material
- H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M10/00—Secondary cells; Manufacture thereof
- H01M10/05—Accumulators with non-aqueous electrolyte
- H01M10/052—Li-accumulators
- H01M10/0525—Rocking-chair batteries, i.e. batteries with lithium insertion or intercalation in both electrodes; Lithium-ion batteries
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M4/00—Electrodes
- H01M4/02—Electrodes composed of, or comprising, active material
- H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
- H01M4/131—Electrodes based on mixed oxides or hydroxides, or on mixtures of oxides or hydroxides, e.g. LiCoOx
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M4/00—Electrodes
- H01M4/02—Electrodes composed of, or comprising, active material
- H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
- H01M4/134—Electrodes based on metals, Si or alloys
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M4/00—Electrodes
- H01M4/02—Electrodes composed of, or comprising, active material
- H01M4/36—Selection of substances as active materials, active masses, active liquids
- H01M4/362—Composites
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- H—ELECTRICITY
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- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M4/00—Electrodes
- H01M4/02—Electrodes composed of, or comprising, active material
- H01M2004/021—Physical characteristics, e.g. porosity, surface area
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M4/00—Electrodes
- H01M4/02—Electrodes composed of, or comprising, active material
- H01M2004/026—Electrodes composed of, or comprising, active material characterised by the polarity
- H01M2004/027—Negative electrodes
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M4/00—Electrodes
- H01M4/02—Electrodes composed of, or comprising, active material
- H01M4/36—Selection of substances as active materials, active masses, active liquids
- H01M4/48—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides
- H01M4/485—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of mixed oxides or hydroxides for inserting or intercalating light metals, e.g. LiTi2O4 or LiTi2OxFy
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
- Y02E60/10—Energy storage using batteries
Definitions
- the present invention provides a non-aqueous electrolyte secondary battery.
- an organic film called SEI Solid Electrolyte Interface
- SEI Solid Electrolyte Interface
- the negative electrode containing lithium titanium composite oxide as a negative electrode active material has almost no SEI formed on the surface thereof. That is, this negative electrode active material is always in direct contact with the non-aqueous electrolyte. For this reason, a side reaction tends to occur between the negative electrode active material and the non-aqueous electrolyte, and self-discharge easily occurs.
- the present invention provides a non-aqueous electrolyte secondary battery in which self-discharge is greatly suppressed while maintaining discharge characteristics and rapid charging performance at a large current.
- a positive electrode, a negative electrode spatially separated from the positive electrode, and a non-aqueous electrolyte are provided, and the negative electrode is formed on a current collector and at least one surface of the current collector.
- a non-aqueous electrolyte secondary battery is provided.
- the present invention it is possible to provide a non-aqueous electrolyte secondary battery in which self-discharge is significantly suppressed while maintaining discharge characteristics and rapid charge performance at a large current.
- FIG. 2 is an XPS spectrum diagram on the surface of a negative electrode layer of a sample sampled from the negative electrode of Example 1.
- FIG. 2 is a photograph taken by a digital camera on the surface of a negative electrode layer of a sample sampled from the negative electrode of Example 1.
- FIG. 2 is a photograph taken by a digital camera on the surface of a negative electrode layer of a sample sampled from the negative electrode of Example 1.
- the non-aqueous electrolyte secondary battery according to the embodiment includes a positive electrode, a negative electrode spatially separated from the positive electrode, and a non-aqueous electrolyte.
- Negative electrode The negative electrode is formed on a current collector, one or both surfaces of the current collector, and an active material or conductive material whose potential based on metallic lithium at the time of lithium insertion / extraction is 0.5 V or more and 2 V or less.
- a negative electrode layer containing an agent and a binder. On the surface of the negative electrode layer, 10-80% of metallic iron is formed per unit area.
- metallic iron is added to the negative electrode layer containing an active material (for example, titanium composite oxide) whose potential based on metallic lithium at the time of insertion / extraction of lithium is 0.5 V or more and 2 V or less per unit area.
- an active material for example, titanium composite oxide
- the area where the negative electrode layer surface and the non-aqueous electrolyte are in direct contact can be reduced.
- the reaction between the titanium composite oxide contained in the negative electrode layer and the non-aqueous electrolyte can be suppressed, self-discharge of the non-aqueous electrolyte secondary battery including the negative electrode having the negative electrode layer can be suppressed. Can do.
- the inventors aimed to achieve the same effect by forming 10 to 80% of nickel, manganese or cobalt other than iron on the surface of the negative electrode layer per unit area.
- the above-mentioned metals other than iron do not show the self-discharge suppressing effect but promote self-discharge.
- the reason why iron was effective is not yet clear.
- metals other than iron have a catalytic effect of promoting the reaction between the titanium composite oxide and the non-aqueous electrolyte, while iron is simply formed on the surface of the negative electrode layer, and the titanium composite oxide. It was confirmed that the reaction between the product and the non-aqueous electrolyte was suppressed, and no other adverse effect was observed.
- Examples of the active material having a potential based on metallic lithium at the time of insertion / extraction of lithium of 0.5 V or more and 2 V or less include antimony intermetallic compound, lithium molybdenum oxide, and lithium lanthanum niobium oxide.
- Preferred active materials include lithium titanium composite oxide having a spinel crystal structure of titanium composite oxide and non-patent literature (R. Marchand, L. Brohan, M. Tournoux, Material Research Bulletin 15, 1129 (1980)). It is TiO 2 (B) of the described titanium dioxide.
- the most preferable titanium-based oxide is a spinel type lithium titanium oxide having a composition of Li 4 Ti 5 O 12 .
- the metallic iron formed on the negative electrode layer surface is less than 10% per unit area, it is difficult to exhibit a sufficient self-discharge suppressing effect. If the metallic iron formed on the surface of the negative electrode layer exceeds 80% per unit area, the diffusion of lithium ions is inhibited when lithium is inserted into or extracted from the negative electrode layer. As a result, there is a risk of impairing the discharge characteristics and rapid charging performance at high currents. More preferably, the metallic iron formed on the surface of the negative electrode layer is 30 to 70%, more preferably 40 to 60% per unit area.
- metallic iron on the surface of the negative electrode layer
- a method using lithium iron phosphate as an active material of the positive electrode can be mentioned.
- lithium iron phosphate is used as the positive electrode active material
- a small amount of water contained in the non-aqueous electrolyte secondary battery reacts with lithium iron phosphate, and iron ions are eluted from the positive electrode into the non-aqueous electrolyte.
- the eluted iron ions diffuse to the negative electrode side and are deposited on the negative electrode layer surface as a metallic iron element (hereinafter referred to as metallic iron).
- the amount of metallic iron deposited that is, the formation ratio of metallic iron per unit area on the surface of the negative electrode layer can be controlled by changing the conditions of the aging treatment after the production of the battery. Specifically, the aging process is performed by adjusting the battery to a certain charging depth (StateSof Charge; SOC) and leaving it at a constant temperature for a certain period.
- SOC charging depth
- Lithium iron phosphate refers to a substance represented by the composition formula LiFePO 4 having an olivine type crystal structure as a main component.
- a carbon coating may be applied to the surface of the active material particles of the positive electrode, or a minute amount of metal may be substituted for Fe in the crystal structure.
- various oxides such as MgO and ZrO 2 may be coated on the surface of LiFePO 4 .
- the metallic iron is preferably formed on the surface of the negative electrode layer in a sea / island state.
- the island state is a metal iron covered region
- the sea state is a metal iron uncovered region
- the sea state metal iron covered region is simply referred to as an island region
- the sea state metal iron uncovered region is simply referred to as a sea region).
- the sea region functions as a lithium ion diffusion path to the negative electrode layer surface, it is possible to maintain good discharge characteristics and rapid charge performance at a large current.
- the island region cuts off the contact between the negative electrode layer surface and the non-aqueous electrolyte, so that self-discharge can be effectively suppressed.
- one or more sea regions having an area of 50 mm 2 or less exist within a 4 cm 2 field of view of the negative electrode layer surface.
- the individual sea region has an area of 0.1 mm 2 or more and 50 mm 2 or less. It is more preferable that 1 to 75 sea areas having such an area exist within the 4 cm 2 field of view. It is further preferred that the sea area having an area of 0.1 mm 2 or more 50 mm 2 or less are present 50 or less 5 or more in the field of view.
- the closest distance between the sea areas having the area is preferably 0.1 to 5 mm.
- lithium ion diffusion is considered to be slower than in the sea area. Therefore, for example, when the island region and the sea region are localized, the diffusion of lithium ions is also likely to be localized. As a result, the charge / discharge reaction region of the opposing positive electrode is likely to be localized, which may deteriorate the cycle characteristics. In addition, localization of the lithium diffusion region may deteriorate discharge characteristics and rapid charge performance at a large current. Therefore, it is preferable that the island region and the sea region exist in a distributed manner over the entire electrode surface.
- Such a form of sea state and island state of metallic iron can uniformly disperse the sea region and the island region. As a result, good performance can be maintained in terms of cycle characteristics, discharge characteristics at a large current, and rapid charging performance.
- the contact blocking portion (island region) between the surface of the negative electrode layer and the non-aqueous electrolyte is not localized but dispersed, so that self-discharge can be more effectively suppressed.
- the island region preferably has a maximum height of 1 nm to 100 nm.
- the maximum height refers to the height from this sea level to the highest point of the island area when the sea surface is a metallic iron uncovered area (sea area). If the height of the island region is less than 1 nm, it is difficult to achieve the desired self-discharge suppression effect. When the height of the island region exceeds 100 nm, metallic iron may penetrate the separator between the positive electrode and the negative electrode, causing an internal short circuit.
- the negative electrode layer is more likely to have a gradually decreasing region between the island region and the sea region.
- the area of the lithium ion diffusion path with respect to the surface can be effectively increased. As a result, it is possible to maintain even better discharge characteristics at high current and quick charge performance.
- Carbon material is usually used for the conductive agent.
- the carbon material only needs to have high alkali metal occlusion and conductivity.
- Examples of the carbon material include acetylene black or carbon black.
- binder examples include polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF), fluorine-based rubber, ethylene-butadiene rubber (SBR), polypropylene (PP), polyethylene (PE), and carboxymethyl cellulose (CMC).
- PTFE polytetrafluoroethylene
- PVdF polyvinylidene fluoride
- SBR ethylene-butadiene rubber
- PP polypropylene
- PE polyethylene
- CMC carboxymethyl cellulose
- the blending ratio of the active material, the conductive agent and the binder is preferably 70 to 95% by weight of the negative electrode active material, 0 to 25% by weight of the conductive agent, and 2 to 10% by weight of the binder.
- Positive electrode includes, for example, a current collector and a positive electrode layer that is formed on one or both surfaces of the current collector and includes an active material, a conductive agent, and a binder.
- lithium iron phosphate alone or a mixture of lithium iron phosphate and various oxides, sulfides, lithium composite oxides, and lithium composite phosphate compounds can be used.
- active materials other than lithium iron phosphate include lithium manganese composite oxide (eg, LiMn 2 O 4 or LiMnO 2 ), lithium nickel composite oxide (eg, LiNiO 2 ), lithium cobalt composite oxide (LiCoO 2 ), lithium Nickel-cobalt composite oxide (for example, LiNi 1-x Co x O 2 , 0 ⁇ x ⁇ 1), lithium manganese cobalt composite oxide (for example, LiMn 2-x Co x O 4 , 0 ⁇ x ⁇ 1), lithium composite phosphorus An acid compound (for example, LiMn x Fe 1-x PO 4 , 0 ⁇ x ⁇ 1).
- Examples of the conductive agent include acetylene black, carbon black, and graphite.
- binder examples include polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF), fluorine-based rubber, ethylene-butadiene rubber (SBR), polypropylene (PP), polyethylene (PE), and carboxymethyl cellulose (CMC).
- PTFE polytetrafluoroethylene
- PVdF polyvinylidene fluoride
- SBR ethylene-butadiene rubber
- PP polypropylene
- PE polyethylene
- CMC carboxymethyl cellulose
- the mixing ratio of the active material, the conductive agent and the binder is preferably 80 to 95% by weight of the active material, 3 to 20% by weight of the conductive agent, and 2 to 7% by weight of the binder.
- Non-aqueous electrolyte is prepared by dissolving an electrolyte in a non-aqueous solvent.
- non-aqueous solvent a known non-aqueous solvent for lithium batteries can be used.
- non-aqueous solvents include cyclic carbonates such as ethylene carbonate (EC) and propylene carbonate (PC); mixed solvents of cyclic carbonate and a non-aqueous solvent having a viscosity lower than that of the cyclic carbonate (hereinafter referred to as second solvent).
- second solvent mixed solvents of cyclic carbonate and a non-aqueous solvent having a viscosity lower than that of the cyclic carbonate
- second solvents are linear carbonates such as dimethyl carbonate, methyl ethyl carbonate or diethyl carbonate; ⁇ -butyrolactone, acetonitrile, methyl propionate, ethyl propionate; cyclic ethers such as tetrahydrofuran or 2-methyltetrahydrofuran; Includes chain ethers such as dimethoxyethane or diethoxyethane.
- Examples of the electrolyte include alkali salts, and lithium salts are particularly preferable.
- Examples of lithium salts include lithium hexafluorophosphate (LiPF 6 ), lithium tetrafluoroborate (LiBF 4 ), lithium hexafluoroarsenide (LiAsF 6 ), lithium perchlorate (LiClO 4 ), or trifluorometa Lithium sulfonate (LiCF 3 SO 3 ) is included.
- lithium hexafluorophosphate (LiPF 6 ) and lithium tetrafluoroborate (LiBF 4 ) are preferable.
- the electrolyte is preferably dissolved at 0.5 to 2 mol / L in the non-aqueous solvent.
- the separator is for preventing the positive electrode and the negative electrode from coming into contact, and is made of an insulating material. Furthermore, a shape in which the electrolyte can move between the positive electrode and the negative electrode is used. Specifically, for example, a synthetic resin nonwoven fabric, a polyethylene porous film, a polypropylene porous film, or a cellulose-based separator can be used.
- FIG. 1 is a partial cross-sectional view showing a cylindrical nonaqueous electrolyte secondary battery.
- the bottomed cylindrical container 1 made of, for example, stainless steel also serving as the negative electrode terminal has an insulator 2 disposed at the bottom.
- the electrode group 3 is accommodated in the container 1.
- the electrode group 3 is produced by winding the positive electrode 4 and the negative electrode 6 in a spiral shape with a separator 5 interposed therebetween.
- the negative electrode 6 includes a current collector (not shown) and an active material that is formed on both surfaces of the current collector and has a lithium metal reference potential of 0.5 V or more and 2 V or less at the time of lithium insertion / extraction,
- a negative electrode layer (not shown) including a conductive agent and a binder. On the surface of the negative electrode layer, 10-80% of metallic iron is formed per unit area.
- Non-aqueous electrolyte is contained in the container 1.
- the insulating paper 7 having an open center is disposed above the electrode group 3 in the container 1.
- the insulating sealing plate 8 is fixed to the upper opening of the container 1 by caulking.
- the positive terminal 9 is fitted in the center of the insulating sealing plate 8.
- the positive electrode lead 10 has one end connected to the positive electrode 4 and the other end connected to the positive electrode terminal 9.
- the negative electrode 6 is connected to a container 1 that also serves as a negative electrode terminal through a negative electrode lead (not shown).
- FIG. 2 shows a partially cutaway perspective view of a thin non-aqueous electrolyte secondary battery.
- the flat electrode group 11 has a structure in which a positive electrode 12 and a negative electrode 13 are flattened with a separator 14 interposed therebetween.
- the negative electrode 13 has the same structure as the negative electrode 6 described in FIG.
- the strip-like positive electrode terminal 15 is electrically connected to the positive electrode 12.
- the strip-like negative electrode terminal 16 is electrically connected to the negative electrode 13.
- the electrode group 11 is housed in a laminated film-made outer bag 17 with the end portions of the positive electrode terminal 15 and the negative electrode terminal 16 extending from the outer bag 17.
- the nonaqueous electrolytic solution is accommodated in the laminated film outer bag 17.
- the laminated film outer bag 17 has the opening 11 sealed with the electrode group 11 and the non-aqueous electrolyte by heat sealing together with the positive electrode terminal 15 and the negative electrode terminal 16.
- Example 1 Preparation of positive electrode> First, 91% by weight of lithium iron phosphate (LiFePO 4 ) powder as an active material, 2.5% by weight of acetylene black, 3% by weight of graphite, and 3.5% by weight of polyvinylidene fluoride (PVdF) are added to N-methylpyrrolidone. In addition, a slurry was prepared by mixing. The slurry was applied to an aluminum foil (current collector) having a thickness of 15 ⁇ m, dried, and pressed to produce a positive electrode having a positive electrode layer with a density of 2.5 g / cm 3 .
- LiFePO 4 lithium iron phosphate
- PVdF polyvinylidene fluoride
- a slurry was prepared by adding 85% by weight of spinel type lithium titanium composite oxide (Li 4 Ti 5 O 12 ) powder, 5% by weight of graphite, 3% by weight of acetylene black and 7% by weight of PVdF and mixing them with NMP.
- the slurry was applied to an aluminum foil (current collector) having a thickness of 11 ⁇ m, dried, and pressed to prepare a negative electrode having a negative electrode layer having a density of 2.0 g / cm 3 .
- Electrode group ⁇ Production of electrode group>
- the positive electrode, a separator made of a polyethylene porous film, the negative electrode, and the separator were each laminated in this order, and then wound in a spiral shape so that the negative electrode was located on the outermost periphery, thereby producing an electrode group.
- Ethylene carbonate (EC) and methyl ethyl carbonate (MEC) were mixed at a volume ratio of 1: 2 to obtain a mixed solvent.
- a non-aqueous electrolyte was prepared by dissolving 1.0 mol / L of lithium hexafluorophosphate (LiPF 6 ) in this mixed solvent.
- the electrode group and the non-aqueous electrolyte were each stored in a stainless steel bottomed cylindrical container. Subsequently, one end of the negative electrode lead was connected to the negative electrode of the electrode group, and the other end was connected to a bottomed cylindrical container that also served as the negative electrode terminal. Subsequently, an insulating sealing plate having a positive terminal fitted in the center was prepared. After connecting one end of the positive electrode lead to the positive electrode terminal and the other end to the positive electrode of the electrode group, the insulating sealing plate is caulked to the upper opening of the container to have the structure shown in FIG. A cylindrical non-aqueous electrolyte secondary battery having a capacity of 5 mm was assembled.
- the obtained secondary battery was charged at 2.4 V in a 0.2 C rate and 25 ° C. environment, and then discharged at a 0.2 C rate until 1 V was reached. After repeating this cycle three times, the battery was charged at a 1C rate so that the charge depth (SOC) was 50% (half charge). Thereafter, storage was performed for 1 day in an 80 ° C. environment with an SOC of 40% (aging treatment). After the aging was completed, charging / discharging was repeated once at a 1C rate in an environment of 25 ° C.
- 1C is a current value required to completely discharge the unit cell in one hour, and for convenience, the nominal capacity value of the unit cell can be replaced with the 1C current value.
- FIG. 3 shows a representative XPS spectrum diagram in the sample.
- FIG. 3 shows an XPS spectrum when metallic iron is not deposited, in addition to an XPS spectrum when metallic iron is deposited. Even when there is no deposition of metallic iron, a broad peak is observed at 710 to 720 eV because the influence of fluorine contained in the electrolyte cannot be excluded.
- FIG. 4 The part A shown in FIG. 4 is a sea area, and the part B is an island area. From this photograph, an island region and a sea region that protruded on the surface of the negative electrode layer were confirmed.
- Surface analysis was performed by Auger spectroscopy (AES) on the island region and the surrounding area. As a result, the presence of Fe element was clarified in the island region.
- the sea region was cut out and the surface was analyzed by the same Auger spectroscopy (AES). As a result, the Fe element was below the detection limit.
- AES Auger spectroscopy
- the coated area of metallic iron calculated for each sample was added, divided by 10 (number of samples), and further divided by 4 cm 2 to obtain the coated area of metallic iron on the negative electrode layer surface of the negative electrode. As a result, the coated area of metallic iron was 51%.
- region was measured by AES from the photography photograph (4 cm 2 visual field) of ten samples. As a result, the maximum height of the island region was 67 nm. In addition, it was confirmed that there is a gradual decrease area where the height changes gently between the island area and the sea area.
- Example 2 A secondary battery similar to that of Example 1 was produced except that the aging treatment described in Table 1 was performed. As in Example 1, XPS, AES, and negative electrode photography were performed. As a result, the form of metallic iron deposited on the negative electrode as in Example 1 was confirmed. The results of the ratio of metallic iron coated on the surface of the negative electrode layer calculated in Example 1, the number of metallic iron non-coated regions, and the maximum height of the coated region are summarized in Table 1.
- Example 1 A nonaqueous electrolyte secondary battery was assembled in the same manner as in Example 1 except that lithium cobalt oxide (LiCoO 2 ) was used as the positive electrode active material and no aging treatment was performed.
- LiCoO 2 lithium cobalt oxide
- the obtained secondary batteries of Examples 1 to 10 and Comparative Example 1 were 100% charged at a 1C rate, and then stored at 45 ° C. for 1 month. Thereafter, a discharge test was performed at a 1 C rate up to 1 V without charging in an environment of 25 ° C., and the remaining capacity of the battery was measured. The remaining rate (%) of the measured remaining capacity of the battery with respect to the remaining capacity of the battery was determined based on the discharge capacity when discharged at a 1C rate in advance before storage.
- the obtained secondary batteries of Examples 1 to 10 and Comparative Example 1 were made 100% charged at a 1C rate, and then a 1C rate and 5C rate discharge test (discharge test at a large current) up to 1V was performed. . At this time, the capacity of the 5C rate relative to the 1C rate was determined as the capacity maintenance rate (%). These results are shown in Table 2 below.
- the nonaqueous electrolyte secondary batteries of Examples 1 to 10 have a high discharge rate remaining before and after storage while maintaining a large current discharge characteristic, that is, self-discharge. It can be seen that can be greatly suppressed.
- the present invention is not limited to the above-described embodiment as it is, and can be embodied by modifying constituent elements without departing from the scope of the invention in the implementation stage.
- various inventions can be formed by appropriately combining a plurality of components disclosed in the embodiment. For example, some components may be deleted from all the components shown in the embodiment.
- constituent elements over different embodiments may be appropriately combined.
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Abstract
Description
負極は、集電体と、この集電体の片面または両面に形成され、リチウムの挿入・脱離時の金属リチウム基準の電位が0.5V以上、2V以下である活物質、導電剤および結着剤を含む負極層とを備える。負極層表面には、金属鉄が単位面積あたり10~80%形成されている。
負極層表面に金属鉄を形成する形態において、金属鉄は前記負極層表面に海・島の状態で形成することが好ましい。ここで、島状態は金属鉄被覆領域 で、海状態は金属鉄非被覆領域 である(以下島状態の金属鉄被覆領域を単に島領域、海状態の金属鉄非被覆領域を単に海領域とする)。海領域は、負極層表面に対するリチウムイオンの拡散パスとして機能するため、良好な大電流時の放電特性および急速充電性能を維持できる。同時に、島領域は負極層表面と非水電解液との接触を遮断するため、自己放電を効果的に抑制することができる。
正極は、例えば集電体と、この集電体の片面または両面に形成され、活物質、導電剤および結着剤を含む正極層とを備える。
前記非水電解液は、非水溶媒に電解質を溶解することにより調製される。
<正極の作製>
まず、活物質であるリチウムリン酸鉄(LiFePO4)粉末91重量%とアセチレンブラック2.5重量%とグラファイト3重量%とポリフッ化ビニリデン(PVdF)3.5重量%とをN-メチルピロリドンに加えて混合してスラリーを調製した。このスラリーを厚さ15μmのアルミニウム箔(集電体)に塗布し、乾燥後、プレスすることにより密度2.5g/cm3の正極層を有する正極を作製した。
まず、スピネル型リチウムチタン複合酸化物(Li4Ti5O12)粉末85重量%とグラファイト5重量%とアセチレンブラック3重量%とPVdF7重量%とをNMPに加えて混合してスラリーを調製した。このスラリーを厚さ11μmのアルミニウム箔(集電体)に塗布し、乾燥し、プレスすることにより密度2.0g/cm3の負極層を有する負極を作製した。
前記正極、ポリエチレン製多孔質フィルムからなるセパレータ、前記負極および前記セパレータをそれぞれこの順序で積層した後、前記負極が最外周に位置するように渦巻き状に巻回して電極群を作製した。
エチレンカーボネート(EC)とメチルエチルカーボネート(MEC)とを体積比で1:2になるように混合して混合溶媒とした。この混合溶媒に六フッ化リン酸リチウム(LiPF6)を1.0モル/L溶解して非水電解液を調製した。
表1記載のエージング処理を行ったこと以外は実施例1と同様な二次電池を作製した。実施例1同様に、XPS、AES、負極の写真撮影を行った。その結果、実施例1と同様な負極への金属鉄堆積形態を確認した。なお、実施例1で算出した負極層表面に被覆された金属鉄の割合、金属鉄非被覆領域の個数、被覆領域の最大高さの結果については、表1にまとめて記載した。
正極の活物質としてリチウムコバルト酸化物(LiCoO2)を用い、エージング処理を全く行わなかったこと以外、実施例1と同様な方法で非水電解液二次電池を組立てた。
得られた実施例1~10および比較例1の二次電池について、1Cレートにて100%充電状態にし、その後45℃環境下で1ヶ月間貯蔵した。その後、25℃の環境下にて、充電せずに1Vまで1Cレートにて放電試験を行って、電池の残存容量を測定した。測定した電池の残存容量を貯蔵前に予め1Cレートで放電したときの放電容量を基準とした電池残存容量に対する残存率(%)を求めた。
Claims (7)
- 正極と、前記正極に空間的に離間された負極と、非水電解液とを具備し、
前記負極は、集電体とこの集電体の少なくとも一方の面に形成され、リチウムの挿入・脱離時の金属リチウムを基準とした電位が0.5V以上、2V以下である活物質を含む負極層とを備え、かつ
前記負極層表面には、金属鉄が単位面積あたり10~80%形成される非水電解液二次電池。 - 前記活物質は、チタン複合酸化物である請求項1記載の非水電解液二次電池。
- 前記金属鉄は、前記負極層表面に海・島の状態で形成され、前記島状態が金属鉄被覆領域、前記海状態が金属鉄非被覆領域である請求項1記載の非水電解液二次電池。
- 前記負極層表面の任意位置で観察した4cm2の視野内において、50mm2以下の面積を持つ前記海状態の金属鉄非被覆領域が1個以上存在する請求項3記載の非水電解液二次電池。
- 前記島状態の金属鉄被覆領域は、1nm以上100nm以下の高さを有する請求項3記載の非水電解液二次電池。
- 前記島状態の金属鉄被覆領域は隆起し、この隆起形状を持つ島状態の金属鉄被覆領域から海状態の金属鉄非被覆領域に向けて厚さが漸減する領域を存在させる請求項3記載の非水電解液二次電池。
- 700eV以上730eV以下の範囲のXPSスペクトル測定において、金属鉄に帰属される704~707eVまたは716~720eVのいずれかに最大のピークを有することを特徴とする請求項1記載の非水電解質二次電池。
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JP2011524582A JP5380537B2 (ja) | 2009-07-30 | 2009-07-30 | 非水電解液二次電池 |
PCT/JP2009/063575 WO2011013228A1 (ja) | 2009-07-30 | 2009-07-30 | 非水電解液二次電池 |
CN200980159019.8A CN102414873B (zh) | 2009-07-30 | 2009-07-30 | 非水电解液二次电池 |
US13/360,293 US20120183849A1 (en) | 2009-07-30 | 2012-01-27 | Non-aqueous electrolyte secondary battery |
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WO2012171450A1 (zh) * | 2011-06-11 | 2012-12-20 | 苏州宝时得电动工具有限公司 | 电极复合材料及其制备方法、正极、具有该正极的电池 |
US10439226B2 (en) * | 2016-04-06 | 2019-10-08 | Kabushiki Kaisha Toshiba | Nonaqueous electrolyte battery, battery pack, and vehicle |
CN116314611B (zh) * | 2023-05-11 | 2023-08-18 | 中创新航科技集团股份有限公司 | 一种锂离子电池 |
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CN102414873B (zh) | 2014-10-01 |
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